The magnetoresistance effect, the phenomenon in which the resistance of an element of certain materials increases with applied magnetic field normal to the direction of current flow in the element, has long been known. This effect depends on the Lorenz force that tends to deflect charge carriers (holes and electrons) moving in an appropriate material, such as a semiconductive crystal, in an electric field and a transverse magnetic field, and is sometimes described as the Hall effect.
A variety of devices have been proposed based on this effect and a paper entitled "Recent Development of Magnetoresistive Devices and Applications" published by Shoer Kataoka in The Circulars of the Electrotechnical Laboratory, No. 182 (December, 1974) describes a number of such devices and their basic principles. In particular, there are described therein magnetodiodes using silicon and germanium. A magnetodiode typically is formed by locating heavily doped p-type and n-type regions spaced apart in a top surface of a lightly doped crystal of silicon and lapping the bottom surface of the crystal to make such bottom surface a high recombination velocity region, i.e., a region where charge carriers of one sign readily recombine with charge carriers of the opposite sign and so both become no longer available for use in conduction. With such a device, the magnetic field to be sensed is made to deflect injected charge carriers into a recombination region whereby the resistance measured between the p-type and n-type regions is reduced because of the fewer charge carriers flowing between the two regions.
In the prior art, some devices of this kind have used a silicon element that is relatively thin, typically no greater than about thirty microns, and whose back surface has been lapped to form the recombination region. Such devices are not readily produced on a mass production basis and so tend to be expensive. Alternatively, other devices of this kind have involved a silicon element grown on a sapphire substrate in which the silicon-sapphire interface is used as a region of high recombination velocity.
A magnetic field being sensed is made to deflect injected carriers towards this interface for recombination so that the number effective for conduction is correspondingly reduced. Devices of this kind are described by A. Chovet et al, in an article entitled "Noise Limitations of Magnetodiodes," Sensors and Activators 4, 1983, pages 147-150 (based on a paper presented at Solid-State Transducers 83, Delft, The Netherlands, May 31-June 3, 1983) and in an article by O.S. Lutes et al, entitled "Sensitivity Limits SOS Magnetodiodes," IEEE Transaction on Electron Devices, ED-27, 1980, pages 2156 and 2157. Such devices tend to be complex and expensive because they involve silicon-on-sapphire technology.
As another alternative, silicon magnetic sensors have been formed composed of two integrated PIN diodes in which a magnetic field being sensed is made to deflect carriers from flowing in one diode to the other diode (see letter by M. Kimura and S. Takahashi entitled "Si Magnetic sensor Composed of Two Combined PIN Diodes," Electronic Letters. 31st, July, 1986, Vol. 22 No. 16). This usually adds to the circuit complexity.
It is desirable to have a magnetodiode, typically of silicon, that can be made using relatively conventional silicon integrated circuit processing techniques, and as such is capable of mass production at low cost.